The prophylactic treatment for potential exposure to Lyme is a single dose of doxycycline within 72 hours of being bitten: https://www.cdc.gov/lyme/resources/pdfs/lyme-pep-low-ink-p.p...

If you catch it early before it takes hold, the treatment is almost inconsequential. If you delay, it's up to a 4 week course of antibiotics.